这JAVA JDBC对象是什么意思
接口：

package db;

import java.sql.Connection;
import java.sql.SQLException;

public interface DBSource {
public Connection getConnection() throws SQLException;
public void closeConnection(Connection conn) throws SQLException;
}

接口实现类：

package db;

import java.io.FileInputStream;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Properties;

public class SimpleDBSource implements DBSource {
private Properties props;
private String url;
private String user;
private String password;

public SimpleDBSource() throws IOException,ClassNotFoundException{
this("jdbc.properties");
}
public SimpleDBSource(String configFile) throws IOException,ClassNotFoundException{
props = new Properties();
props.load(new FileInputStream(configFile));
url = props.getProperty("url");
user = props.getProperty("user");
password = props.getProperty("password");

Class.forName(props.getProperty("driver"));
}
public Connection getConnection() throws SQLException{
return DriverManager.getConnection(url,user,password);
}
public void closeConnection(Connection conn) throws SQLException{
conn.close();
}
}


测试类：

package db;

import java.io.IOException;
import java.sql.Connection;
import java.sql.SQLException;

public class ConnectionDemo {
public static void main(String args[]){
try{

DBSource dbSource = new SimpleDBSource();
Connection conn = dbSource.getConnection();
if(!conn.isClosed()){
System.out.println("数据库已连接上");
}
dbSource.closeConnection(conn);
if(conn.isClosed()){
System.out.println("");
}
}catch(IOException e){
e.printStackTrace();
}catch(ClassNotFoundException e){
e.printStackTrace();
}catch(SQLException e){
e.printStackTrace();
}
}
}

这是书上的一个例子，有点不太明白，各位大哥，想问一下上面这个测试类中的DBSource dbSource = new SimpleDBSource();Connection conn = dbSource.getConnection();这两个是什么意思，我一直看不明白，能否详细解释一下啊，还有为什么要这样声明对象的，

------解决方案--------------------
上面这个测试类中的DBSource dbSource = new SimpleDBSource();Connection conn = dbSource.getConnection();
因为 SimpleDBSource 实现 DBSource接口 ，所以 SimpleDBSource的实例可以赋值给 DBSource接口的引用 ，dbSource.getConnection();--java虚拟机 会自动匹配具体是那个实现类的getConnection方法